Individuals may receive severe head and spinal cord injuries necessitating the use of halo-type traction tools, braces and devices for the treatment of their injuries. The use of halo-type cervical traction devices is known and described in U.S. Pat. No. 3,072,118 to R. G. Standerwick, et al.
Generally, a plurality of anchoring devices are required to be attached to the halo-type traction tool or brace which typically is anchored to the bone of an individual's skull, during the treatment of spinal fractures or injuries and facial reconstruction surgery. Various types of halo and anchoring tools and devices are known, an example of which includes U.S. Pat. No. 4,838,264 to Bremer, et al. Generally, anchoring bone-penetrating skull pins are set in the halo and rotatingly driven axially into the skull bone with a torque device in order to affix a halo-type traction tool to an individual's skull for anchoring further devices.
It is important to note that severe injury may occur if the skull pin goes into the skull too far. Bremer's skull pins have attempted to implement a torque sensitive safety feature which includes the shearing of the handle from the pin engaging cap upon reaching to a predetermined level of torque. This shearing action results in two pieces of the torque limiting device.
There is a need for a torque limiting device for use and in combination with skull pins and halo-traction tools which has not one, but two, shear safety features to prevent skull penetration by the pin or screw causing severe injury. Such a torque limiting device should also remain in one piece for easy handling by the surgeon and also to prevent lose of component parts which is problematic with the prior art.